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An underwater vehicle is provided to move in various orientations and
directions, including pitch, yaw, roll, heave, surge and sway. The
underwater vehicle comprises an upper body and a lower body, wherein both
bodies are separated by two rudders. One rudder is positioned towards the
fore of the underwater vehicle, while the other is positioned towards the
aft. Each rudder forms the basis of a propulsion system, such that the
underwater vehicle has at least two independently controlled propulsion
systems. Each propulsion system further comprises an elevator extending
horizontally from the sides of each rudder and a thrust generator
attached to the elevator. The elevator and thrust generator are able to
pitch about an axis extending horizontally through the sides of the
rudder, and the rudder is able to yaw about an axis extending vertically
through the top and bottom of said rudder.

1. An underwater propulsion system comprising at least one assembly
comprising a rudder configured to be rotatably connected to a hull of an
underwater vehicle to permit rotation of said rudder with respect to said
hull, an elevator pivotally attached to said rudder to pitch about an
axis perpendicular to the axis of rotation of said rudder, and a thrust
generator extending from and attached to said elevator such that said
thrust generator pitches with said elevator.

2. The underwater propulsion system of claim 1 further comprising a
pressurized housing located within said rudder.

3. The underwater propulsion system of claim 2 wherein said thrust
generator comprises a propeller and a motor for driving said propeller.

4. The underwater propulsion system of claim 3 wherein said motor is
controlled by a motor controller, said motor controller located in said
pressurized housing.

5. The underwater propulsion system according to claim 3 wherein said
motor is located within a housing and said propeller is positioned
mid-way along said housing.

6. The underwater propulsion system according to claim 3 wherein said
motor is located within a housing and said propeller is positioned
towards the end of said housing.

7. The underwater propulsion system of claim 2 wherein said elevator is
actuated by a motor, said motor located in said pressurized housing.

8. The underwater propulsion system of claim 7 wherein said motor is
controlled by a motor controller, said motor controller located in said
pressurized housing.

9. The underwater propulsion system according to claim 1 wherein said
rudder is connectable to said hull of said underwater vehicle by a hollow
shaft, said rudder able to rotate about said hollow shaft.

10. The underwater propulsion according to claim 1 wherein one or more
sections of space defined within said rudder are free-flooding.

11. The underwater propulsion system of claim 10 wherein said rudder
comprises one or more drainage holes fluidly connecting said one or more
sections with said rudder's exterior, said one or more holes located
along a surface of said rudder facing said hull.

12. The underwater propulsion according to claim 1 wherein one or more
sections of space defined within said elevator are free-flooding.

13. The underwater propulsion system according to claim 1 wherein said
rudder is rotatably connectable at both ends to different portions of
said underwater vehicle.

14. The underwater propulsion system according to claim 1 wherein said
elevator comprises a starboard plane positioned towards the right of said
rudder and a portside plane positioned towards the left of said rudder,
and each said starboard and portside planes able to move independently
from one another.

15. The underwater propulsion system according to claim 1 wherein said
underwater propulsion system is able to be oriented on to its side so
that said rudder functions to control the pitch of said underwater
vehicle and said elevator functions to control the yaw of said underwater
vehicle.

16. An underwater vehicle comprising: a first body and a second body
positioned in spaced relation to one another and separated by at least
one propulsion system; and each of said at least one propulsion system
comprising: a vertically oriented rudder configured to be rotatably
connected between said first and second bodies and is fully rotatable
about an axis of rotation; an elevator pivotally attached to said rudder
to pitch about an axis perpendicular to the axis of rotation of said
rudder; and a thrust generator extending from and attached to said
elevator such that said thrust generator pitches with said elevator.

17. The underwater vehicle according to claim 16 wherein said first body
is positioned vertically above said second body.

18. The underwater vehicle according to claim 17 wherein said second body
is more buoyant than said first body.

19. The underwater vehicle according to claim 16 wherein either said
first body or said second body houses a vehicle control unit for
controlling said at least one propulsion assembly.

20. The underwater vehicle according to claim 19 further comprising a
hollow shaft extending between said first body and said second body, said
rudder rotating about said shaft.

21. The underwater vehicle according to claim 20 further comprising
cabling routed through said hollow shaft from any one of said upper body
and said lower body.

22. The underwater vehicle according to claim 16 wherein two propulsion
systems are connected to and separate the first body and the second body.

23. The underwater vehicle according to claim 22 wherein an aft
propulsion system is positioned towards the aft of the underwater vehicle
and a fore propulsion system is positioned towards the fore of the
underwater vehicle.

24. The underwater vehicle according to claim 23 further comprising
computer executable instructions for executing a zero-radius turn when
said fore propulsion system's rudder faces either starboard or portside,
and said aft propulsion system's rudder faces the other of either
starboard or portside.

25. The underwater vehicle according to claim 23 further comprising
computer executable instructions for executing a crabbing manoeuvre when
said fore propulsion system's rudder faces either starboard or portside,
and said aft propulsion system's rudder faces the same orientation.

[0002] The following relates generally to propulsions systems for marine
vehicles, and has particular utility when applied to underwater vehicles.

DESCRIPTION OF THE RELATED ART

[0003] In the field of marine vehicles, a vehicle may be propelled using
one or more fixed rear thrusters and the vehicle's orientation and
positioning may be controlled using various control surfaces mounted to
the hull of the vehicle. The flow of water across the control surfaces
generates a force depending on the orientation of the control surface,
and thus a force on the vehicle itself. Such an arrangement may be
suitable when the vehicle is moving at sufficiently high speeds, wherein
a greater force is generated as more water flows over the control
surfaces.

[0004] At slower speeds, generally less water flows over the control
surfaces, thereby reducing the force directed to control the vehicle. The
reduced force generated by the control surfaces affects the performance
of underwater vehicles when carrying out hovering manoeuvres. During a
hovering manoeuvre, an underwater vehicle may maintain a generally fixed
position and orientation of the vehicle's hull for some time period,
while compensating for the effects of cross-currents. This
manoeuvrability may be used in various underwater operations, including
without limitation, inspections that may involve high-detail imaging
equipment and robotic manipulations that may involve precise movements.

[0005] Differential thrust systems may be used to produce a hover in
low-speed underwater conditions. Generally, a differential thrust system
may comprise several thrusters that are mounted at strategic locations
around a vehicle and these thrusters are aimed in certain directions,
allowing the vehicle to have some percentage of its total available
thrust act in any direction. By varying the magnitude of thrust from each
of the thrusters, a vehicle may be able to manoeuvre in various
dimensions. Many remotely operated underwater vehicles (ROVs) may make
use of differential thrust systems.

[0006] The differential thrust system for propulsion allows for hovering
for inspection and intervention in low speed applications and
environments. The differential thrusters also suitably compensate for
cross-current conditions while maintaining an absolute heading.

[0007] There are many configurations that strive to optimize the
positioning of differential thrusters for increased control, such as
positioning each of the differential thrusters away from vehicle's hull.
However, many of such configurations may also reduce the hydrodynamic
streamlining of the underwater vehicle, thereby leading to a loss in
energy efficiency.

[0008] In many cases, the reduced operational and travel efficiency is
compensated by tethering the underwater vehicle, wherein the tether
provides some form of energy to the vehicle. As a result, an underwater
vehicle's travel distance and path is limited to the length of the
tether. Moreover, the above design considerations can add additional cost
and complexity to an underwater vehicle.

[0009] It is an object of the following to provide a propulsion system
that is configured to address the above issues.

SUMMARY OF THE INVENTION

[0010] In one aspect, there is provided an underwater propulsion system
comprising at least one assembly comprising a rudder configured to be
rotatably connected to the hull of an underwater vehicle to permit
complete rotation of the rudder with respect to the hull, an elevator
pivotally attached to the rudder to pitch about an axis perpendicular to
the axis of rotation of the rudder, and a thrust generator extending from
and attached to the elevator such that the thrust generator pitches with
the elevator.

[0011] In another aspect, there is provided an underwater vehicle
comprising: a first body and a second body positioned in spaced relation
to one another and separated by at least one propulsion assembly; and the
at least one propulsion assembly, each propulsion assembly comprising: a
vertically oriented rudder configured to be rotatably connected between
the upper and lower bodies and is fully rotatable about an axis of
rotation; an elevator pivotally attached to the rudder to pitch about an
axis perpendicular to the axis of rotation of the rudder; and a thrust
generator extending from and attached to the elevator such that the
thrust generator pitches with the elevator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments will now be described by way of example only with
reference to the appended drawings wherein:

[0013] FIG. 1a is a perspective view of an exemplary underwater vehicle.

[0014] FIG. 1b is a top planar view of the underwater vehicle shown in
FIG. 1a.

[0015] FIG. 2 is a perspective view in isolation of the exemplary
propulsion system shown in FIG. 1a.

[0016] FIG. 3 is a block diagram of an exemplary embodiment of an
underwater vehicle and propulsion system.

[0017] FIG. 4 is a perspective view of the propulsion system similar to
FIG. 2 and showing various internal components shown schematically in
FIG. 3.

[0018] FIG. 5a is a top planar view of top and bottom cross sections of
the rudder, shown in FIG. 2.

[0019] FIG. 5b is a top planar view of a middle cross section of the
rudder, shown in FIG. 2.

[0020] FIG. 6 is a top planar view in isolation of the propulsion system
shown in FIG. 2.

[0021] FIG. 7 is a profile view of a partial cross section of another
embodiment of a propulsion system shown in isolation.

[0022] FIG. 8 is a profile view of a partial cross section of yet another
embodiment of a propulsion system shown in isolation.

[0023] FIG. 9 is a perspective view of another embodiment of an exemplary
underwater vehicle deployed in an underwater environment.

[0024] FIG. 10 is a perspective view of the underwater vehicle shown in
FIG. 9 while heaving, surging and pitching.

[0025] FIG. 11a is a perspective view of the rotational axes of the
underwater vehicle shown in FIG. 10, relative to the underwater vehicle's
reference frame axes.

[0026] FIG. 11b is a profile view of the rotational axes of the underwater
vehicle shown in FIG. 10, relative to the underwater vehicle's reference
frame axes.

[0027] FIG. 11c is a planar view of the rotational axes of the underwater
vehicle shown in FIG. 10, relative to the underwater vehicle's reference
frame axes.

[0028] FIG. 12 is a perspective view of the underwater vehicle shown in
FIG. 9 while heaving.

[0029] FIG. 13a is a perspective view of the rotational axes of the
underwater vehicle shown in FIG. 12, relative to the underwater vehicle's
reference frame axes.

[0030] FIG. 13b is a profile view of the rotational axes of the underwater
vehicle shown in FIG. 12, relative to the underwater vehicle's reference
frame axes.

[0031] FIG. 13c is a planar view of the rotational axes of the underwater
vehicle shown in FIG. 12, relative to the underwater vehicle's reference
frame axes.

[0032] FIG. 14 is a perspective view of the underwater vehicle shown in
FIG. 9 while yawing.

[0033] FIG. 15a is a perspective view of the rotational axes of the
underwater vehicle 3 shown in FIG. 14, relative to the underwater
vehicle's reference frame axes.

[0034] FIG. 15b is a profile view of the rotational axes of the underwater
vehicle shown in FIG. 14, relative to the underwater vehicle's reference
frame axes.

[0035] FIG. 15c is a planar view of the rotational axes of the underwater
vehicle shown in FIG. 14, relative to the underwater vehicle's reference
frame axes.

[0036] FIG. 16 is a perspective view of an underwater vehicle shown in a
hovering manoeuvre.

[0037] FIG. 17 is a perspective view of an underwater vehicle shown in a
zero-turn radius manoeuvre.

[0038] FIG. 18 is a perspective view of an underwater vehicle shown in a
"crabbing" manoeuvre.

[0039] FIG. 19 is a profile view of another embodiment of an underwater
vehicle shown with clam shell fairings and nose cone fairings.

[0040] FIG. 20 is a profile view of the underwater vehicle shown in FIG.
19 shown with the clam shell fairings removed.

[0041] FIG. 21 is a profile view of the underwater vehicle shown in FIG.
19 shown with the clam shell fairings and the nose cone fairings removed.

[0042] FIG. 22 is a perspective view of a frame of an underwater vehicle.

[0043] FIG. 23 is a perspective view of another embodiment of a frame of
an underwater vehicle.

[0044] FIG. 24 is profile view of a partial cross section of the
underwater vehicle shown in FIG. 19 showing various components therein.

[0045] FIG. 25 is a schematic block diagram of an example propulsion
control system.

[0046] FIG. 26 is a block diagram illustrating various modules implemented
by a software architecture used by the propulsion control system.

[0047] FIG. 27 is a process diagram illustrating various processes
implemented by the software architecture in FIG. 26.

[0048] FIG. 28 is a process diagram illustrating further detail for the
mission processor shown in FIG. 26.

[0049] FIG. 29 is a control logic diagram illustrating use of pitch
feedback.

[0050] FIG. 30 is a control logic diagram illustrating use of depth
feedback.

[0051] FIG. 31 is a control logic diagram illustrating use of heading
feedback.

[0052] FIG. 32 is a control logic diagram illustrating use of velocity
feedback.

[0053] FIG. 33 is a control logic diagram illustrating use of distance
feedback.

DETAILED DESCRIPTION

[0054] It will be appreciated that for simplicity and clarity of
illustration, where considered appropriate, reference numerals may be
repeated among the figures to indicate corresponding or analogous
elements. In addition, numerous specific details are set forth in order
to provide a thorough understanding of the embodiments described herein.
However, it will be understood by those of ordinary skill in the art that
the embodiments described herein may be practiced without these specific
details. In other instances, well-known methods, procedures and
components have not been described in detail so as not to obscure the
embodiments described herein. Also, the description is not to be
considered as limiting the scope of the embodiments described herein.

[0055] Generally, underwater vehicles comprise a body or hull to transport
various loads while protecting the loads from a submersed marine
environment. Various loads may include without limitation, scientific
equipment, people and components required to operate the underwater
vehicle. The body or hull of a vehicle may protect the loads from the
effects of the water, including wetting, and hydrostatic and hydrodynamic
pressure. Typically a propulsion unit attached to the body is used to
move the body in certain directions.

[0056] FIG. 1a shows an underwater vehicle 3 comprising two bodies or
hulls, an upper body 2 and a lower body 4. It is noted that the terms
`body` and `hull` refer to the same structure, as described in more
detail below. Both bodies 2, 4 comprise an oblong-shaped geometry for
streamlining. In the particular embodiment shown in the FIG. 1a, both the
upper and lower bodies 2, 4 comprise a cylindrical hull having the end
portions rounded to reduce hydrodynamic resistance. It is noted that the
front end, or nose, of each body 2, 4 may comprise a more hemispherical
geometry, while the rear end, or tail, may comprise a more conical
geometry. This profiled geometry allows for reduced water drag. The
purpose of each body or hull 2, 4 is to house various loads while
streamlining the flow of water over the surface of each body or hull 2, 4
and that any means of doing so are encompassed within the various
possible configurations for the underwater vehicle 3.

[0057] Turning to FIG. 1b, a top planar view of the underwater vehicle 3
is shown in context with directional terminology. The front of the
underwater vehicle 3 is referred to as the fore and the rear is referred
to as the aft. From the perspective of a person on the underwater vehicle
3 facing towards the fore, the left-hand side is referred to as the
portside, while the right-hand side is referred to as the starboard.

[0058] Returning to FIG. 1a, the underwater vehicle 3 is propelled by at
least two propulsion systems, denoted 5a for the fore propulsion system
and 5b for the aft propulsion system. For continued clarity of the
description, suffix `a` herein refers to the fore portion of the
underwater vehicle 3 and suffix `b` refers to the aft portion. The upper
body 2 is positioned directly above the lower body 4 and extending
vertically between the two bodies 2,4 are a pair of rudders 6a, 6b. In
the embodiment shown in FIG. 1a, a fore rudder 6a is positioned towards
the front of the underwater vehicle 3 and an aft rudder 6b is positioned
towards the back of the underwater vehicle 3. Both the fore rudder 6a and
aft rudder 6b comprise rigid structures that position the upper body 2 at
a fixed distance from the lower body 4. It is appreciated that a rudder 6
is a control surface that affects the yaw of the underwater vehicle 3.
Both rudders 6a, 6b are able to yaw independently of each other, as
indicated by the movement arrows 16a and 16b. The fore and aft
positioning of the rudders 6a, 6b and the independent direction of yaw
forces generated from the fore rudder 6a and aft rudder 6b allow for
manoeuvres of various complexities as discussed further below.

[0059] In this example, the purpose of each rudder 6 is to act as a
control surface affecting the yaw, and any configuration capable of doing
so is encompassed by the embodiments described herein.

[0060] The two rudders 6a, 6b form a structural base for the underwater
vehicle's propulsion system 5a, 5b, respectively, which further comprises
respective elevators 12 and thrusters 14. An elevator 12 protrudes from
both sides of a rudder 6 and comprises a rigid control surface or plane
that is generally perpendicular to the rudder 6. The flow of fluid over
the elevator 12 generates forces that affect the pitch or inclination of
the underwater vehicle 3. Each elevator 12 is able to rotate or pitch, as
indicated by the movement arrows 18a and 18b. In the embodiment shown in
FIG. 1a, both the fore elevator 12a and aft elevator 12b have a swept
wing geometry to reduce drag. It is understood that elevators 12
comprising other geometries to control the pitch while reducing drag are
equally applicable.

[0061] Similar to the rudders 6a, 6b, both the fore elevator 12a and aft
elevator 12b are able to move independently from one another. In one
example, the fore elevator 12a may pitch downwards, while the aft
elevator 12b may pitch upwards to create a coupled moment, thereby
pitching the underwater vehicle 3 downwards. The fore and aft positioning
of the elevators 12a, 12b and the independent direction of pitch forces
generated from the fore elevator 12a and aft elevator 12b allow for
manoeuvres of various complexities as discussed further below.

[0062] In another embodiment, each of the elevators 12 can be defined by a
starboard elevator component and a portside elevator component. The
starboard elevator component of an elevator 12 may be able to pitch
independently from the portside elevator component, thereby providing
further manoeuvrability. It is understood that each of the starboard
elevator component and the portside elevator component would be actuated
by separate motors for independent control and movement.

[0063] It is noted that all control planes (i.e. rudder 6 and elevator 12)
advantageously use NACA 00xx airfoil profiles, an industry standard in
naval architecture. The NACA 00xx airfoil profiles provide hydrodynamic
efficiency and geometrical convenience. It will be appreciated that other
airfoil profiles that allow for the same are equally applicable.

[0064] Fixed to each elevator 12 is a thrust generator 14, such that the
thrust generator 14 is oriented with the same pitch as the elevator
moves. Since each elevator 12 is fixed to a rudder 6, the elevator 12
and, therefore the thrust generator 14, will also be oriented to have the
same yaw as the rudder 6. The thrust generator 14 is located behind the
trailing edge of the rudder 6 so as to allow for a larger range of pitch
rotation, while avoiding interference between the thrust generator 14 and
rudder 6. Other configurations between the thrust generator 14, elevator
12, and rudder 6 that allow the thrust generator to move across a
sufficient range for pitch and yaw are equally applicable.

[0065] The thrust generator 14 shown in FIG. 1a, comprises a single
propeller driven by a motor. Other embodiments of a thrust generator 14
may include one more motors driving one or more propellers.
Alternatively, a thrust generator 14 may comprise the release of a
pressurized gas or liquid. It is appreciated that any mechanisms for
generating thrust are equally applicable.

[0066] The direction of the force generated by the thrust generator 14 is
indicated by the direction arrows 20a and 20b. The coupling of a thrust
generator 14 to the elevator 12 and rudder 6, allows the thrust generator
14 to direct the thrust at various pitch and yaw angles. The independent
movement of the fore and aft thrust generators 14a, 14b, and the
positioning of the thrust generators 14a, 14b in relation to the upper
and lower bodies 2, 4 allow the underwater vehicle 3 to carry out complex
manoeuvres, discussed in further detail below.

[0067] Turning to FIG. 2, a perspective view of an isolated propulsion
system 5 is shown in greater detail. The thrust generator 14, in one
embodiment shown in FIG. 2, comprises a propeller 24 driven by a motor
assembly 22. The motor 22 may be located external to the rudder 6 and
elevator 12 to allow the thrust generator 14 to rotate or pitch relative
to the rudder 6. In addition to increased range of rotation, placing the
motor 22 external to the rudder 6 and elevator 12 reduces the complexity
of transferring the motor's energy to the propeller 24. The motor
assembly 22 is fixed to a U-shaped bracket 26, and more particularly to
the portion that bridges the two armatures of the bracket 26. Each
armature on the bracket 26 is situated between the elevator 12 and rudder
6. The bracket 26 is fixed to the elevator 12, wherein the pitch movement
of the elevator 12 and, therefore, the thrust generator 14 may be
identical. The bracket 26 also positions the propeller 24 further away
from the trailing edge of the rudder 6, thereby allowing the thrust
generator 14, in this case the propeller 14, to achieve a larger range of
pitch rotation. It is appreciated that alternate configurations of the
propeller 14, motor 22 and bracket 26 that allow for a sufficient range
of rotation are equally applicable.

[0068] Also shown in FIG. 2 is an XYZ reference frame that in this example
is fixed relative to the underwater vehicle 3 body for the purpose of
describing the various configurations below. The XYZ reference frame is
oriented such that the X axis is oriented along the length of the vehicle
and is directed toward the rear or aft of the vehicle. The Z axis is
oriented vertically between the upper body 2 and lower body 4, such that
the Z axis is aligned with the vertical length of the rudder 6, and is
directed upwards toward the upper body 2. The Y axis is oriented
perpendicular to both X and Z axes and, in accordance with chirality, is
directed towards the starboard side of the underwater vehicle 3 in this
example. This reference may be used to describe the axes of rotation for
the above components.

[0069] The propeller 24 rotates about the axis A. The axis A, in this
case, extends along the length of the bracket 25 and motor assembly 22.
The axis A and the elevator 12 both rotate, or pitch, about axis B. It is
appreciated that the A axis rotates with the elevator 12 about axis B
since the bracket 25 and motor assembly 22 are fixed to the elevator 12.
It is further understood that rotational axes A and B remain
perpendicular to one another. Axes A and B, and the rudder 6 rotate, or
yaw, about axis C.

[0070] The three rotational axes, A, B, and C, introduced above, may be
described relative to the underwater vehicle's XYZ reference frame. In a
neutral orientation, the underwater vehicle's control surfaces are
oriented such that the underwater vehicle 3 is directed in a straight
heading, with no yawing or pitching movements. In this neutral
orientation, the rotational axis A is parallel with the X axis. The A
axis is oriented towards the back or aft of the underwater vehicle 3 in
the same direction with the X axis, which is also oriented towards the
back or aft of the vehicle. In a neutral orientation, the rotational axis
B is oriented parallel to the Y axis. However, according to the
convention shown here, the positive B axis is oriented towards the
portside of the underwater vehicle 3 and the positive Y axis is oriented
towards the starboard side of the underwater vehicle 3. The rotational
axis C always remains oriented parallel and in the same direction as the
vertical Z axis when using this reference frame.

[0071] It is noted that the A axis may pitch about the B axis by some
angle +/-alpha (.alpha.). It is also understood that the thrust from the
thrust generator 14 is directed along the A axis. For example, when the A
axis inclines above the X axis by +alpha, the elevator 12 and direction
of thrust is pitched in a downward direction. Similarly in another
example, when the A axis declines below the X axis by--alpha, the
elevator 12 and the direction of thrust is pitched in an upward
direction. It is further appreciated that when the thrust is directed in
along the X axis, then the thrust is directed towards the aft of the
underwater vehicle 3, thereby propelling or pushing the underwater
vehicle 3 forward.

[0072] With regard to the yaw movement, both A and B axes, as well as the
rudder 6, may pivot about axis C by some angle +/-beta (.beta.). For
example, when the propulsion system or assembly 5 yaws by +beta, the
rudder 6 and the A axis rotate from the X axis in a counter clockwise
direction. Similarly, the B axis rotates from the -Y axis in a counter
clockwise direction by +beta. In yet another example, when the propulsion
assembly 5 yaws by -beta, the trailing edge of the rudder 6 and the A
axis rotate from the X axis in a clockwise direction, and the B axis
rotates from the -Y axis in a clockwise direction. It can be appreciated
that the propulsion system 5 may yaw about the C axis by 360 degrees in
either a clockwise or counter clockwise direction. As will be exemplified
below, such freedom of rotation about the C axis enables complex and
controlled movements that provides greater handling and control of an
underwater vehicle 3.

[0073] The combined movements of the pitch and yaw allows the axis A, and
therefore thrust vector, to be oriented in various directions. The
combination of the two or more in-line propulsion systems 5 with the
described underwater vehicle 3 allow for various manoeuvres with five
degrees of freedom, including pitch, yaw, heave (i.e. moving up and
down), surge (i.e. moving forward and backward) and sway (i.e. moving
left and right).

[0074] It may be noted that roll movements may also be achieved if the
elevators 12 are controlled to pitch in opposite directions. For example,
if the starboard elevators were to pitch upwards and the portside
elevators were to pitch downwards, then the underwater vehicle 3 may tend
to roll towards the portside.

[0075] In another embodiment, not shown, the underwater vehicle 3
comprises at least a first and a second body, whereby the bodies are
adjacent to one another and are separated by at least one propulsion
system 5. In other words, instead of having an upper and lower body 2, 4
as described above, there is a left and a right body. The underwater
vehicle 3 shown in FIG. 1a, for example, would be rolled 90 degrees on to
its side. In this orientation, the rudder 6 separating the first and
second bodies, or the left and right bodies, becomes an elevator.
Similarly, the elevator 12 shown in FIG. 1a becomes a rudder. Therefore,
when the underwater propulsion system 5 is oriented on to its side, the
rudder 6 functions to control the pitch of the underwater vehicle 3 and
the elevator 12 functions to control the yaw of the underwater vehicle 3.
It can thus be appreciated that underwater vehicle 3 and the propulsion
system 5 may have various orientations and configurations.

[0076] Turning to FIG. 3, the various components in the propulsion system
5 are shown schematically. The rudder 6 subassembly, elevator 12
subassembly and thrust generator 14 subassembly each comprise a motor 30,
36, 42, motor controller 28, 34, 40 and gearbox 32, 38, 44. In general,
each motor controller 28, 34, 40 receives signals from a vehicle control
unit 48 through a network communication system 46. The motor controller
28, 34, 40 then actuates its corresponding motor 30, 36, 42, which may be
coupled to a gearbox 32, 38, 44, to modify the speed and power output of
the motor 30, 36, 42.

[0077] The vehicle control unit 48 is preferably a computer, housed in the
upper body 2 of the underwater vehicle 3, which contains the vehicle's
control system software (not shown but can be appreciated as any computer
instructions, data structures, memory and other software components
stored on and/or accessible from a computer readable medium). It can be
appreciated that the vehicle control unit may be housed in lower body 4
as well. Based on navigational sensor input (e.g. GPS, DVL, Altimeter,
Attitude Sensor) and using pre-programmed mission criteria, the control
system software may calculate the desired vehicle speed, pitch, roll, and
heading. Then, based on the current speed, pitch, roll, and heading, the
control system sends control information via a network communication
system 46, such as a controller-area network (i.e. CAN) bus (as shown in
FIG. 3), to the respective motor controllers 28, 34, 40 for each rudder
6, elevator 12 and thrust generator 14 to achieve the desired
orientation.

[0078] The sub-assemblies in FIG. 3 are indicated by the dashed lines,
while the outer solid lines indicate the pressure housings. The rudder
subassembly, comprising the rudder's motor controller 28, motor 30 and
gearbox 32, is completely contained within its own pressure housing,
located in the upper body 2 of the underwater vehicle 3. Components from
the elevator and thrust generator subsystem share a pressure housing
located in the rudder 6. The elevator's motor controller 34, motor 36 and
gearbox 38, as well as the thrust generator's motor controller 40 are
located within the pressurized portion of the rudder 6. The thrust
generator's motor 42 and gearbox 44 are located external to the rudder 6
and elevator 12 in a separate pressure housing 22 fixed to the end of the
bracket 26. The purpose of placing the above components in various
pressure housings is to protect the above components from the effects of
the water while reducing mechanical complexity.

[0079] FIG. 4 shows various ones of the above components when housed in
the physical structures. In this embodiment, the rudder 6 is divided into
three logical and physical sections; the top 52, middle 54, and bottom 56
sections. The top 52 and bottom 56 sections are free-flooding to allow
for water to enter and exit freely through designated drainage holes. The
drainage holes are positioned in certain areas along the airfoil of the
rudder 6 to maintain hydrodynamic efficiency. In one embodiment, the
drainage holes may be placed along the top and bottom surfaces of the
rudder 6, wherein the top surface is adjacent to the underside of the
upper body 2 and the bottom surface is adjacent to the topside of the
lower body 4. In other words, the drainage holes are located on a surface
of the rudder that faces the hull of the underwater vehicle 3. The middle
section 54 of the rudder 6 is pressurized to house the elevator's motor
controller 34, motor 36 and gearbox 38, as well as the thrust generator's
motor controller 40. The middle section 54 may also be referred to as a
pressurized housing. It can be appreciated that the top 52 and bottom 56
sections of the rudder 6 are free-flooding to reduce the effects of
dynamic shifting buoyancy forces on the underwater vehicle 3.

[0080] Cabling from the upper body 2 to the lower body 4 may also be
routed through the hollow shaft 50 around which the rudder 6 rotates.
Cabling from the upper body 2 to the respective elevators 12 and thrust
generators 14 on the rudder 6 is also routed through this hollow shaft 50
to the components in the pressure housings, which require access to power
and the communication network 46.

[0081] In this embodiment, the rudder's top 52 and bottom 56 sections are
almost identical or mirror images of each other except for one difference
pertaining to the joints. The joint from the top section 52 to the upper
body 6 contains the motor 30 for rotating the rudder 6, whereas the joint
from the bottom section 56 to the lower body 4 contains a bearing to
allow for smooth yaw movement.

[0082] The geometry and functionality of the rudder's middle section 54
differ from the top 52 and bottom 56 sections, although it is
mechanically attached to the other two sections. The profile of a top 52
or bottom 56 section, shown in FIG. 5a, comprises a rounded leading edge
and a pointed trailing edge. The front face of the middle section 54 is
curved to match the nose radius of the airfoil-like profile of the
rudder's top 52 and bottom 56 sections. However, as shown in FIG. 5b, the
trailing edge portion of the rudder's middle section 54 has a different
rectangular profile instead of a pointed edge.

[0083] Returning to FIG. 4, the rectangular profile towards the trailing
edge increases the volume within the middle section 54 of the rudder 6
and, therefore, allows room for components, such as motor controllers 34,
40, to be stored within the pressure housing. At least one shaft 58
extends horizontally through the middle section, via two waterproof shaft
seals, connecting the elevator motor 36 and gearbox 38 to the elevator
planes 12. The rotation of the horizontal shaft 58 may cause the elevator
planes 12 to pitch. It may be noted that the horizontal shaft 58
corresponds to the rotational axis B. The elevator 12 may be composed of
two identical planes, attached on either side of the rudder's middle
section 54 via the horizontal shaft 58, as well as the attached bracket
26 used for mounting the motor assembly 22 and propeller 24 aft of the
two planes.

[0084] FIG. 4 also illustrates where the elevator planes may be connected
and aligned together, such that one motor 36 is required to actuate both
planes of the elevator 12. A single motor configuration reduces power
consumption, reduces complexity and reduces the amount of space required.
Alternatively, in another embodiment, the starboard plane and portside
plane may each be coupled to their own separate motor for independent
control. Therefore, the two separate motors may facilitate rolling
movement.

[0085] It may be noted that both planes in the elevator 12 do not contain
pressure housings, and are free-flooding. Similar to the rudder 6,
drainage holes are provided to allow water to enter and exit the elevator
12, and the holes are placed along the elevator 12 to maintain
hydrodynamic efficiency. In one embodiment, the drainage holes are placed
on the face of the elevator plane 12 attached to the bracket 26 and
further, coincident with an identical hole in the bracket 26 itself. This
embodiment allows water to enter and/or exit through the drainage holes
in the elevator 12, through the coincident holes in the attached bracket
26. The elevator 12 is free-flooding to reduce the effects of shifting
buoyancy forces on the underwater vehicle 3. As the elevator 12 extends
away from the centerline of the underwater vehicle 3, and pitches and
yaws in various directions, the effects of positioning a pressurised
housing, or buoyancy generator, may be avoided by flooding the elevator
12 structure. It is noted that the effects of positioning a pressurised
housing in the elevator 12 may comprise changes in resulting moments and
force vectors acting on the underwater vehicle 3 during various
manoeuvres.

[0086] FIG. 4 further shows the thrust generator 14, which, in one
embodiment, comprises a motor 42 and planetary gearbox 44 mounted inside
a hydrodynamic pressure housing for the motor assembly 22, with a sealed
bearing connecting the output shaft to a large diameter propeller 24. A
cable from the motor assembly housing 22 to the pressurised rudder
housing, or middle section 54, connects the motor 42 to the motor
controller 40. It can be appreciated that the motor controller 40 is
housed in the rudder's pressurised middle section 54 in this example.

[0087] The motor assembly 22 and propeller 24 are mounted to the bracket
26, which is mechanically attached to the elevator planes and placed
slightly aft of the trailing edge of the rudder 6. The angle of rotation
of the elevator 12 is limited to prevent the bracket 26 and propeller 24
from impacting the trailing edge of the rudder 6. Both hard stops,
implemented mechanically, and soft stops, implemented in the vehicle
control unit 48, may be added to prevent impacts.

[0088] FIG. 6 shows the propulsion assembly 5 from a top planar view. Seen
more clearly, the axis A pitches about axis B and yaws about axis C. It
is also noted in this embodiment, the pitch axis B may be offset from the
yaw axis C. This offset is also reflected in the implementation, wherein
the rudder 6 pivots about the vertical hollow shaft 50, which is located
towards the leading edge of the rudder 6. The elevator 12 is attachable
to the rudder 6 by the horizontal shaft 58, which is located further back
from the leading edge of the rudder 6.

[0089] In FIG. 6, the profile of the rudder's middle section 54, which
comprises a rectangular-shaped trailing edge, is also shown relative to
the profile of the rudder's top section 52. In addition, the bracket 26
is shown attached to an inner portion of the elevator 12.

[0090] Turning to FIG. 7, another embodiment of an isolated propulsion
system 5 is provided. The configuration of the components are different
from those shown in FIG. 4. The motor controller 28, motor 30 and gearbox
32 for the rudder 6 are housed separately from the rudder 6, for example,
in the upper body 2 or the lower body 4. The motor controller 40 for the
elevator 12 is positioned within the pressurized housing 70 of the rudder
6 and, in particular, the motor controller 40 is positioned above the
motor 36 and gearbox 38 of the elevator 12. As can be seen, the
pressurized housing 70, shown in dotted lines, extends along the length
of the rudder 6. The remaining space defined within the rudder 6 may be
free-flooded. Also housed within the pressurized housing 70 is the motor
controller 40 for the thrust generator 14. In particular, the thrust
generator 14, is shown to include a propeller 24 that is mounted towards
the end of an tubular housing 72. The tubular housing 72 contains the
motor 42 and gearbox 44 for moving the propeller 24. The propeller 24
shown in FIG. 7 comprises three separate blades suited for underwater
conditions.

[0091] FIG. 8 shows yet another embodiment of a propulsion system 5 in
isolation which is similar to the embodiment in FIG. 7. However, in FIG.
8, both motor controllers 34, 40 for the elevator 12 and the thrust
generator 14 are located side-by-side in the pressure housing 70. It can
be appreciated that the motor controllers 34, 40 may actually reside on a
single physical hardware controller capable of implementing computer
executable instructions to control the elevator motor 36 and the thrust
motor 42. It can also be seen that the propeller 24 is located roughly
mid-way along a cylindrical-shaped housing 74. The housing 74 contains
the motor 42 and gearbox 44 for moving the propeller 24.

[0092] The placement of the propeller 24 roughly mid-way along the length
of the housing 74, as shown in FIG. 8, advantageously increases the range
of rotation for the elevator 12. In particular, placing the root of the
propeller blades toward the end of the housing 72, as per FIG. 7, may
lead to the propeller 24 impacting the upper body 2 or lower body 4 when
the elevator 12 and thrust generator 14 pitches upwards or downwards,
respectively, by a large angle. Therefore, by locating the root of the
propeller blades further towards the rudder 6, sometimes also referred to
as a "foldback" propeller design, the elevator 12 can be pitched upwards
or downwards by a large angle without the propeller 24 impacting the
upper body 2 or lower body 4. In this way, the configuration shown in
FIG. 8 allows for an increased range of rotation (e.g. pitch) in the
elevator 12 and thrust generator 14.

[0093] Turning to FIG. 9, one embodiment of the underwater vehicle 3 in an
underwater environment is shown relative to a seabed 64. In this
embodiment, various sensors 60, for example sonar and imaging equipment,
are located in the lower body 4 and may be used to collect data about the
seabed 64. Some sensors 60 may be positioned in the lower body 4 to allow
for better line-of-sight with the area below the underwater vehicle 3.
Other sensors 60 may also be located in the upper body 2. The upper body
2, for example, may house a wireless communications receiver and
transceiver 62 to communicate with other marine vessels or a base
station. The communications system 62 may relay various information
including for example, control commands and sensor data. The
communications system 62 may relay command signals to the vehicle control
unit 48 to carry out various manoeuvres by orienting the propulsion
system in particular configurations.

[0094] It has also been found that various ones of these components can be
housed in the lower body 4 in order to lower the center of gravity, which
assists in the various movements of the vehicle. By way of background,
when a marine vessel is tilted the center of buoyancy of the vessel moves
laterally. The point at which a vertical line through the tilted center
of buoyancy crosses the line through the original, non-tilted center of
buoyancy is the metacenter. Lowering of the center of gravity increases
the metacentric height, that is the distance between the metacentre and
center of buoyancy. A larger metacentric height increases the natural
stability of the vehicle in pitch and roll.

[0095] It is appreciated that various manoeuvres, many of which utilize
the natural stability of the underwater, may be achieved with one or more
of the described propulsion systems 5 as described below.

[0096] FIG. 10 shows the underwater vehicle 3 with two propulsion systems
5a, 5b. The underwater vehicle 3 is ascending with the length of the
bodies 2, 4 being generally parallel with the flat seabed 64, and having
a slight pitch. This manoeuvre involves the fore elevator 12a and thrust
generator 14a pitching upwards, which causes the nose or front end of the
underwater vehicle 3 to move in an upwardly direction. Simultaneously,
the aft elevator 12b and thrust generator 14b pitch upwards as well,
which also causes the tail or back end of the underwater vehicle 3 to
move in an upwardly direction as well. This combined movement of both the
fore and aft propulsion systems allows the underwater vehicle 3 to move
both forward and upward simultaneously. Alternatively, this manoeuvre may
be characterised by pitch, heave and surge.

[0097] FIGS. 11a to 11c show the perspective view, profile view and planar
view of the rotational axes A, B, and C relative to the underwater
vehicle 3's XYZ reference frame during an upward and forward ascending
manoeuvre, according to FIG. 10. From FIG. 11a, the fore rotational axis
A.sub.1 rotates below the X axis by some angle -.alpha..sub.1 degrees,
thereby directing the thrust downwards. The aft rotational axis A.sub.2
also rotates below the X axis by some angle -.alpha..sub.2 degrees, such
.alpha..sub.2 is slightly less than .alpha..sub.1. Therefore, more thrust
is generally directed downwards towards the fore of the underwater
vehicle 3 compared to the aft, which may cause the overall underwater
vehicle 3 to pitch slightly upwards. The profile view in FIG. 11b also
shows that the A axis has a horizontal component direct along the X axis
and, thus, the some of the force or thrust from the thrust generators
14a, 14b is acting along the X axis to propel the underwater vehicle 3
forward.

[0098] FIG. 11c also shows that no yawing action is involved in this
manoeuvre, since the planar view shows that A.sub.1 and A.sub.2 are still
aligned with X axis, and B.sub.1 and B.sub.2 are still aligned with the
-Y axis. Therefore, rotational angles .beta..sub.1 and .beta..sub.2 both
equal 0.degree..

[0099] Turning now to FIG. 12, the underwater vehicle 3 is shown carrying
out another manoeuvre, such that the underwater vehicle 3 is vertically
translating upwards, or heaving, only. There are no yaw, pitch, roll,
surge and sway movements. This heave manoeuvre may be useful in various
situations. For example, when the underwater vehicle 3 wants to inspect
or navigate with respect to the vertical face of an underwater cliff, the
underwater vehicle 3 may move upwards and downwards along the height of
the cliff while maintaining a fixed horizontal distance from the cliff
face.

[0100] FIGS. 13a to 13c show different views of the orientations of the
rotational axes relative to the XYZ reference frame for the heave-only
manoeuvre. First, the fore propulsion system yaws 180.degree. about the C
axis, such that the leading edge of the fore rudder 6a is directly facing
the leading edge of the aft rudder 6b. This yaw rotation is represented
by the angle .beta..sub.1, which equals 180.degree.. As shown in FIGS.
13a and 13c, after the rotation of .beta..sub.1, the rotational axis
B.sub.1 is aligned and pointed in the same direction as the +Y axis. It
is noted that the aft propulsion system does not yaw and, thus,
.beta..sub.2 equals 0.degree..

[0101] After the first B.sub.1 rotation, FIGS. 13a and 13b show that the
elevator 12 and thrust generator both pitch upwards. Therefore, the
A.sub.1 axis rotates below the -X axis in a counter clockwise direction
by some angle +.alpha..sub.1, and the A.sub.2 axis rotates below by the X
axis in a clockwise direction by some angle -.alpha..sub.2. Assuming the
magnitude of thrust is the same from both thrust generators 14a and 14b,
the pitch angles .alpha..sub.1 and .alpha..sub.2 are equal in order to
cancel out the horizontal forces along the X axis. The horizontal forces
cancel each other out since the thrust generators 14a and 14b are
directed in opposite directions along the X axis, resulting in only
vertical forces. This allows the underwater vehicle 3 to translate
vertically upwards.

[0102] Turning to FIG. 14, the underwater vehicle 3 is shown in the middle
of a turn manoeuvre towards the left or starboard side. The two separate
propulsion systems located at the fore and aft of the underwater vehicle
3 create a coupled moment about the center of the underwater vehicle 3,
which allow for a smaller turning radius. In effect, the underwater
vehicle 3 could yaw about a central point with little forward or lateral
movement. For example, if the fore rudder 6a directs its leading edge to
the face the portside and the aft rudder 6b directs its leading edge to
face the starboard side, then the underwater vehicle 3 may rotate or yaw
in a counter clockwise direction about a point. This manoeuvrability may
be used, for example, to face a forward mounted sensor on the vehicle in
an opposite direction while in an environment with constrained space.

[0103] FIGS. 15a to 15c show the different views of the rotational axes A,
B and C relative to the underwater vehicle 3's XYZ reference frame for a
the starboard turn, according to FIG. 14. It is appreciated that this
manoeuvre does not require any pitching motion and, thus, both fore and
aft elevators 12a, 12b do not rotate about the B axis. As a result
.alpha..sub.1 and .alpha..sub.2 are equal to 0.degree., as shown most
clearly in FIG. 15b.

[0104] FIGS. 15a and 15c show the fore propulsion system yawing by some
angle -.beta..sub.1 in counter clockwise direction about the C.sub.1
axis. The rotational axis A1 rotates away from the X axis by
-.beta..sub.1, and the rotational axis B.sub.1 rotates away from the -Y
axis by -.beta..sub.1. It is noted that in this embodiment, the
rotational axes A and B remain perpendicular to one another. With this
clockwise rotation, the leading edge of the fore rudder 6a is directed
towards the starboard side and the thrust is directed towards the
portside. This causes the nose of the vehicle to turn towards the right
or starboard.

[0105] Similarly, the aft propulsion system yaws by some angle
.beta..sub.2 in a clockwise direction about the C.sub.2 axis. The
rotational axis A2 rotates away from the X axis by .beta..sub.2, and the
rotational axis B2 rotates away from the -Y axis by .beta..sub.2. It is
noted that in this embodiment, the rotational axes A and B remain
perpendicular to one another. With this counter clockwise rotation, the
leading edge of the aft rudder 6b is directed towards the portside and
the thrust is directed towards the starboard. This causes the tail end of
the vehicle to turn towards the left or portside. In this example
manoeuvre, the angle .beta..sub.2 is less than the angle .beta..sub.1
and, thus, the nose of the underwater vehicle 3 turns more quickly to the
starboard than the tail end turns to the portside.

[0106] There may be various combinations of pitch and yaw that allow for
different movements. For example, if both rudders 6a, 6b direct their
leading edges to the left or portside, then the entire underwater vehicle
3 will sway, or laterally translate, towards the portside. This sway
movement does not require any yawing rotations. Other movements may
include, for example, pitching and yawing simultaneously, or heaving and
yawing simultaneously, or moving backwards and pitching simultaneously.
In a more specific example, the underwater vehicle 3 may maintain a
constant downwards pitch, while moving backwards and side-to-side.
Various combinations of pitch, yaw, heave, surge and sway may be
accomplished with the propulsion system described herein. Furthermore,
with independent starboard and portside elevators, roll may also be
achieved. Therefore, the underwater vehicle 3 may move in all six degrees
of freedom.

[0107] FIGS. 16, 17 and 18 show other configurations of the fore and aft
propulsion systems 5a, 5b which allows the underwater vehicle 3 to
achieve different manoeuvres. FIG. 16 shows the two propulsion systems
5a, 5b in a hovering configuration, whereby the underwater vehicle 3 is
able to heave up or down without swaying, surging or rotating. In
particular, the fore rudder 6a has its leading edge directed to the aft
of the vehicle 3, and the fore elevator 12a is pitched upwards. The aft
rudder 6b has its leading edge directed to the fore of the vehicle 3 and
the aft elevator 12b is pitched upwards. FIG. 17 shows the two propulsion
systems 5a, 5b in a zero-point radius turn configuration, whereby the
underwater vehicle 3 is able to yaw without other types of movement. In
particular, the fore rudder 6a has its leading edge directed to the left
or portside and the aft rudder 6b has its leading edge directed to the
right or starboard. FIG. 18 shows the two propulsion systems 5a, 5b in a
swaying or "crabbing" configuration, whereby the underwater vehicle 3 is
able to translate laterally without other types of movement. In
particular, both rudders 6a, 6b direct their leading edges to the right
or starboard.

[0108] Another advantage in movement is the underwater vehicle 3's ability
to hover, or stay in a fixed position, while maintaining an absolute
heading. The propulsion system 5 also allows the underwater vehicle 3 to
hover in the presence of currents in any direction and of reasonable
speed.

[0109] Different manoeuvres may also be achieved by varying the force
produced by the thrust generators 14. In one manoeuvre, for example, the
fore thrust generator 14 may produce more force during a turn than the
aft thrust generator 14b, thereby causing the nose of the underwater
vehicle 3 to move at a faster speed. This variable thrust may be
generated by increasing or decreasing the speed at which the propeller 24
rotates about the axis A. In addition, the thrust may be varied by
controlling the pitch, or angle of attack, or the propeller's blades.

[0110] Having two or more of the propulsion systems 5 positioned towards
the fore and aft of the underwater vehicle 3 also allows for high
manoeuvrability. This configuration encompasses the advantages of both
thrust vectoring and differential thrusters. Furthermore, by positioning
the two propulsion systems 5 in-line with one another and situated
between the upper body 2 and lower body 4, the drag is reduced and
hydrodynamic efficiency is maintained.

[0111] The configuration of the upper body 2 and lower body 4 also
provides the advantage of increased stability with respect to pitch and
roll. Separating and placing the lower body 4 below the upper body 2,
lowers the center of gravity and provides a higher center of buoyancy.

[0112] FIGS. 19, 20 and 21 show various views and other components of an
embodiment of an underwater vehicle 3. In FIG. 19, the lifting lug 76 is
positioned on the upper body 2 and can be used as an attachment point to
lift or hoist the entire vehicle 3. One or more antennas 78 are also
attached to the upper body 2 and may be used for GPS, radio frequency
signals, or other forms of wireless communication. As can be seen, the
exterior of the upper body 2 and lower body 4 is covered by a clam shell
fairing 80, which is removable to access the inner components. Towards
the fore of the vehicle 3, there are nose cone fairings 84 to protect the
components found within, as well as reduce drag. There are also side-scan
transducers 82 that can be used to measure different aspects of the
underwater vehicles environment 3. The transducers 82 may be positioned
along the length of the lower body 4.

[0113] FIG. 20 shows the underwater vehicle 3 of FIG. 19 with the clam
shell fairings 80 removed. An electronics housing 80 located at the upper
body 2 protects various electrical components. A battery housing 88 is
located at the lower body 4 to lower the center of gravity of the vehicle
3 towards the lower body 4. A payload housing 90 is also shown for
carrying various materials, for example, sensors.

[0114] FIG. 21 shows the underwater vehicle 3 without clam shell fairings
80 and nose cone fairings 84. Certain portions of the underwater vehicle
3 include buoyant material 92 to provide additional buoyancy. In
particular, buoyant material is located in the fore and aft of the upper
body 2, as well as towards the aft of the lower body 4. Examples of
buoyant material may include foam, foam products, air pockets, etc. The
additional buoyancy in the upper body 4 lowers the center of gravity for
the vehicle 3, thereby providing increased roll stability. Located at the
fore of the lower body 4 is an obstacle avoidance sensor 98, which may
be, for example, of the laser, sonar, infrared, or camera type. An
altimeter 96 is also located towards the bottom of the lower body 4. Also
positioned in the lower body 4 is a Doppler-type sensor 94, which can be
used for determining the positioning of the vehicle relative to its
environment. The Doppler-type sensor 94 may be a Doppler velocity Log
device.

[0115] FIGS. 22 and 23 show two separate embodiments of a frame structure
for the underwater vehicle 3. In FIG. 22, an embodiment of a frame 100
includes more ribs and thicker material. In FIG. 23, another embodiment
of frame 102 includes fewer ribs and thinner material, in order to reduce
the weight. The hollow shaft 50, for which a rudder 6 is attached, is
also shown.

[0116] FIG. 24 shows another embodiment of an underwater vehicle 3 whereby
a partial cut-away view of the internal components are displayed. A drop
weight 108 is located in the lower body 4. It can be appreciated that the
drop weight 108 can be released in order to allow the underwater vehicle
3 to ascend more quickly. A camera and a light 106 are located toward the
aft of the lower body 4 and are pointed downwards to gather visual data.
At the upper body 2, a fore fin 110a and an aft fin 110b protrude upwards
for increased stability. Within the electronics housing 86 in the upper
body 4, there are various components including a computer 112, emergency
batteries 114, a wireless modem 116, a GPS device 118, and an acoustic
modem 120. It can be appreciated that various types of electronic devices
may be stored and used within the underwater vehicle 3.

[0117] The electronics of the underwater vehicle are powered by the main
battery 88, which for example is a 48VDC Li-Ion battery pack. There are
also separate DC/DC power supplies for various components. Voltage &
Current monitoring devices ensure that the electrical components (e.g.
motors) are running at normal parameters. A self-resetting fuse is used
to protect the propulsion system components, and other electrical
systems. For example, CAN-based solid state relays disconnect in the
event of a failure or short-circuit. For convenience the batteries 88 and
emergency batteries 114 can be charged within the underwater vehicle 3
and may also be swapped with another battery (e.g. a charged battery).
Failsafe protocols in the electrical hardware and software may also be
used to prevent the electrical system or software from failing. An
example of such a protocol is a process for using the emergency batteries
114 should the main batter 88 lose operational capability.

[0118] It can be appreciated that the underwater vehicle 3 may be
autonomous and able to navigate itself, as well as carry out various
other functions (e.g. collecting data, collecting samples, carrying a
payload). In another embodiment, the underwater vehicle 3 may be
controlled by a pilot positioned within the underwater vehicle 3. In
another embodiment, the underwater vehicle may be partially or completely
piloted by a remote pilot, who is able to send piloting commands
wirelessly or through a tethered cable. One example software architecture
that can be used to autonomously control the underwater vehicle 3 is
provided below.

[0119] Turning now to FIG. 25, another embodiment of the propulsion
control system shown in FIG. 3 is provided. The CAN bus 46 is shown in
greater detail and includes a CANbus I/O interface 146 to interface with
the actuators associated with the forward and aft thrusters 114a, 114b,
the forward and aft elevators 106a, 106b, and the forward and aft rudders
102a, 102b. The VCU 48 is also shown, which is also connected to the CAN
bus 46. Also shown in FIG. 17 are a low-drift clock+GPS unit 152, a
Doppler velocity profiler (DVL) 154, an altimeter 156, and an obstacle
avoidance unit 158, each connected to the CAN bus 46 via a respective
CAN-to-RS232 interface 150. A mission control unit (MCU) 148 is also
shown, which provides connections to an AHRS+GPS unit 160, an acoustic
modem 162, an iridium modem 168, and an Ethernet hub 164. The Ethernet
hub 164 can also provide access to a fibre optic unit 166 and a long
range RF modem 170.

[0120] Shown in FIG. 25 is a modular decentralized architecture that
utilizes CAN-based motor controllers (not shown) for each actuator
associated with a thruster, elevator or rudder. In this example, fully
programmable CAN-based controllers are used to allow for flexible
functionality and a high-degree of task-specific customization. Each
motor controller typically contains a Flash memory for programming
user-defined functions, which may include specific motion control such a
differing acceleration and deceleration rates, or custom functionality
such as special features or input/output control. In this example,
special functions that are particularly useful are for position homing
and loss of communication protection. The actuators (not shown) can use a
Hall-effect sensor based homing algorithm for absolute positioning,
implemented directly on the motor controllers as a user-defined function.
When the motor controller is first powered on, this algorithm seeks the
range limit of the actuator, defined by the Hall-effect sensors, and
calculates the center point between the limits. This algorithm allows for
less-costly relative encoders on the motors while still enabling absolute
position control of the actuators for the underwater vehicle's control
system.

[0121] The actuators interface with the VCU 48 through the CANbus
interface 146, receiving synchronous set-point commands in the form of
CAN messages. If CANbus communications fail, or the VCU 48 software
encounters a fault and stops sending commands, the vehicle actuators
should respond to prevent damage to the underwater vehicle 3 and the
actuators themselves. After evaluating potential solutions, a loss of
communication protection algorithm can be implemented on each motor
controller. Similar to a watchdog timer (WDT), if the motor controller
has not received an updated command within a set time period, if stops
the motor and issues a fault message. Since this functionality is
localized to the motor controller, each actuator has its own individual
protection, independent of the other actuators.

[0122] FIG. 26 illustrates the functional modules for one example software
architecture for the propulsion control system.

[0123] It will be appreciated that any module or component exemplified
herein that executes instructions may include or otherwise have access to
computer readable media such as storage media, computer storage media, or
data storage devices (removable and/or non-removable) such as, for
example, magnetic disks, optical disks, or tape. Computer storage media
may include volatile and non-volatile, removable and non-removable media
implemented in any method or technology for storage of information, such
as computer readable instructions, data structures, program modules, or
other data. Examples of computer storage media include RAM, ROM, EEPROM,
flash memory or other memory technology, CD-ROM, digital versatile disks
(DVD) or other optical storage, magnetic cassettes, magnetic tape,
magnetic disk storage or other magnetic storage devices, or any other
medium which can be used to store the desired information and which can
be accessed by an application, module, or both. Any such computer storage
media may be part of the propulsion control system or accessible or
connectable thereto. Any application or module herein described may be
implemented using computer readable/executable instructions that may be
stored or otherwise held by such computer readable media.

[0124] As shown in FIG. 26 a mission planner module 200 is deployed at the
surface. The surface mission planner module 200 allows an operator at the
surface to control the underwater vehicle 3 manually and to plan missions
and download such missions to the underwater vehicle 3 via a surface
communications module 202. The mission planner module 200 utilizes or
generates a mission plan, which can be in any suitable computer readable
format such as an ASCII file to enable the mission to be specified or
edited using a text editor. Commercially available mission planning
software such as MIMOSA provided by IFREMER (French Research Institute
for Exploration of the Sea) or See Track Offshore provided by See Byte
Ltd. The mission planner module 200 can use a graphical user interface
(GUI)--not shown--designed to enable the operator to enter new missions
and monitor the missions from the surface when they are executed. For
example, a main display can be used to include a bathymetric map of the
area if available. The waypoints in the mission could also be displayed
on such a map. Other information such as status parameters of the
underwater vehicle 3 could also be provided in the GUI. These parameters
may include depth, battery level, communications link status, thruster
status, navigation faults, and payload faults.

[0125] On the underwater vehicle 3, a vehicle communications module 204 is
provided to communicate with the surface communications module 202 to
obtain mission plans and to provide status information and other data
depending on the application. The vehicle communications module 204 in
turn provides the mission plans to a mission processor 206, which
extracts a mission profile from the mission plan and generates a list of
waypoints from the profile. It can be appreciated that waypoints are sets
of coordinates that identify a point in physical space. In one example, a
mission profile can define a ladder survey where the underwater vehicle 3
executes a zig-zag pattern over a specified area. The mission profile
would include waypoints of an area that should be mapped. In another
example, the mission profile can define a pipeline survey where the
underwater vehicle 3 follows a pipeline and maps the surrounding area.
For such a mission, the approximate location of the pipeline would be
specified and the underwater vehicle 3 then descends to this location,
searches for the pipeline using on-board capabilities such as a sonar
system, and then follows the pipeline. As shown in FIG. 26 a payload
module 208 represents a functional module associated with payload such as
a sonar system and receives commands from the mission processor 206 to
operate the payload and provides the data acquired using the payload back
to the mission processor 206.

[0126] A sensor module 210 is also shown, which may represent one or more
sensors that collect data from various sensors mounted on the underwater
vehicle 3. The sensor module 210 passes this data with an associated
timestamp to a vehicle monitor module 212 and an estimator module 218.
Examples of sensors utilized by the underwater vehicle 3 include GPS,
MRU/GPS combination, DVL, altimeter pointing down, altimeter pointing 45
degrees forward, temperature, pressure, etc. The vehicle monitor module
212 monitors the overall vehicle software and status information to
ensure that the underwater vehicle 3 is operating correctly. The vehicle
monitor module 212 should be able to take action if any vehicle component
is not working, e.g. if a navigation failure is encountered, an emergency
surfacing of the underwater vehicle 3 can be executed. The vehicle
monitor module 212 communicates with an electrical distribution module
214 for controlling power to each individual vehicle electrical component
and subsystem through an array of solid state relays (SSRs). The
electrical distribution module 214 responds to inputs from both the
vehicle monitor 212 and the mission processor 206.

[0127] The vehicle monitor module 212 monitors the health and status of
all subsystems and components, through software interfaces (e.g. RS232,
etc.), current and voltage monitoring circuits, and fault sensors (e.g.
leak detectors, ground fault sensors, etc.). If there is a problem with a
particular subsystem or component, such as excessive current being drawn,
the vehicle monitor module 212 may make the decision to disable that
component by sending a command to the electrical distribution module 214
to turn off its relay. Alternatively, there may be a simple software
fault, and a component needs to be "reset", similar to a normal PC, and
the vehicle monitor module 212 can also command that action.

[0128] The mission processor 206 not only produces waypoints for the
trajectory controller for navigational purposes, it also has a
higher-level knowledge of the different stages of a mission, and what
payloads are required for each stage. For example, while the vehicle is
under water, certain systems such as GPS, RF, and satellite
communications are no longer able to be used. Thus, the mission processor
206 commands the electrical distribution module 214 to deactivate these
certain systems to conserve power. Conversely, while the underwater
vehicle 3 is on the surface, it may not require its acoustic modem or
USBL systems, and may deactivate those until the appropriate time.
Finally, the mission processor 206 will command the electrical
distribution module 214 to activate and deactivate payloads as they are
needed, depending on the stage of the mission, as payloads tend to be
significant power consumers.

[0129] A trajectory control module 216 is also provided which obtains the
waypoints from the mission processor 206 and generates a smooth
trajectory to a desired position. For example, a standard heading
tracking algorithm can be used, or if available, an optimal energy
trajectory or fast trajectory algorithm can be applied over one or more
waypoints. A control module 220 receives set points from the trajectory
control module 216 and receives sensor data from the estimator module
218, which calculates the current position, velocity, and attitude of the
underwater vehicle 3. The control module 220 uses the set points and the
current position provided by the estimator module 218 to calculate an
error value between the current position and the position of the
waypoint. This error is used to control the motors 30, 36, 42, to move
the underwater vehicle 3 to the waypoint. As such, motors module 222 are
also provided, which send commands to the motors 30, 36, 42. In the
examples shown herein, the motors module 222 would send commands to six
different motors, three on each of the fore and aft propulsion systems.

[0130] The software architecture herein described should enable the
control and estimator modules 218, 220 to run in real-time and should be
extendible to accommodate new algorithms. The architecture should also be
able to use encrypted communication protocols if required in specific
applications, however such details are not shown herein. The operator
should be able to change the underwater vehicle's mission while a current
mission is in progress, which may require the underwater vehicle 3 to be
on the surface and within communication range, or be within range of an
acoustic data communications link between the surface and the underwater
vehicle 3. The architecture should also have the ability to execute
multiple types of missions, e.g. ladder surveys, pipeline surveys, etc.
Moreover, the operator should have the ability to start and stop
components at runtime, the ability to effect new configuration changes
across all components at runtime, the ability to implement new control
algorithms on the underwater vehicle 3, and provide usability for
different operators having different skill levels.

[0131] A process diagram is shown in FIG. 27, which illustrates how the
various functions and modules shown in FIG. 26 operate together to
accomplish a mission. A surface process 230 can be executed to
communicate with the underwater vehicle 3 and a communication process 232
can be executed to communicate with a surface ship (not shown). A mission
process 234 is then executed to process a mission obtained from the
surface ship, which controls power onboard the underwater vehicle 3 using
an electrical distribution process 236, and enables the calculation of a
trajectory by initiating execution of a trajectory control process 242. A
vehicle monitoring process 238 may also be executed to monitor the health
of the underwater vehicle 3, which obtains sensor values obtained by a
sensor process 240. A control process 244 is executed to calculate the
control gains using the calculated trajectory and calculated positions of
the underwater vehicle 3 provided by an estimator process 246. To then
effect movement of the underwater vehicle 3, the control module then
initiates execution of a motors process 248 to update the motors. It can
be appreciated that the processes shown in FIG. 27 can be implemented
continuously, intermittently, or on demand in order to carry out a
mission or to respond to a specific command (e.g. an override from a
failure detection system or from the surface ship, etc.).

[0132] The surface process 230 runs on a surface computer and allows a
user to control and run missions on the underwater vehicle 3. The
following Table 1 illustrates various example functions that can be
programmed into the software for being executed in the surface process
230.

TABLE-US-00001
TABLE 1
Surface Process Functions
Function Description
initWireless( ) Initialize communication over wireless modem
(connected by Ethernet)
initAcustic( ) Initialize communication over underwater link
initEthernet( ) Initialize communication over Ethernet (fibre or wire
connection)
initSatellite( ) Initialize communication using Satellite modem.
receiveData( ) Receive data through one of the open and initialized
communication ports.
sendData( ) Send data through one of the open and initialized
communication ports.
debugMode( ) Opens up a terminal to allow direct communication
with the underwater vehicle, via the linux command
line. Recommend to be used only when wired link
between the host and underwater vehicle is used.
PlanMission( ) This function allows the operator to plan a mission for
the underwater vehicle. A graphical user interface over
a map is recommended.
ExecuteMission( ) Send mission to underwater vehicle and start
executing mission.
ManualControl( ) Allows the operator to manually control the
underwater vehicle

[0133] The communication process 232 sets up communication with the
surface computer using a modem and an associated communication medium
such as wireless, wired, acoustics, etc. The following Table 2
illustrates various example functions that can be programmed into the
software for being executed in the communication process 232.

TABLE-US-00002
TABLE 2
Communication Process Functions
Function Description
initWireless( ) Initialize communication over wireless modem
(connected by Ethernet)
initAcustic( ) Initialize communication over underwater link
initEthernet( ) Initialize communication over Ethernet (fibre or wire
connection)
initSatellite( ) Initialize communication using Satellite modem.
receiveData( ) Receive data through one of the open and initialized
communication ports.
sendData( ) Send data through one of the open and initialized
communication ports.
debugMode( ) Opens up a terminal to allow direct communication with
the underwater vehicle, via the linux command line.
Should be used only when wired link between the host
and underwatervehicle is used.

[0134] It can be appreciated that, depending on communications link
available, for data sent via the sendData function, the Time and Health
should always be transmitted, and the rest of the data to be transmitted
should be selectable by the operator. The following Table 3 illustrates
an example format for various data types.

[0136] The mission process 234 obtains the mission from the surface and
executes it. It also updates the status of the mission, underwater
vehicle 3 position and underwater vehicle 3 health to the communication
process 232. The mission process can also be used to control the payload
208 (e.g. turns the sonar system on/off depending on the position of the
underwater vehicle 3).

[0137] The mission process 234 is typically the first process that is
started on the underwater vehicle 3. The mission process 234 then starts
the communication process 232 and establishes contact with the host
control. FIG. 28 provides a logic diagram illustrating execution of the
mission process 234. As can be seen in FIG. 28, in this example, the
mission processor 206 executes a direct control process 250, a return to
ship process 252, or a move to waypoint or waypoint mission process 254.
Under the direct control process 250, commands are sent to the motors and
the altimeters can be used to check for obstacles. For the return to ship
process 252, the payload 208 is turned off, the underwater vehicle 3 is
sent to the surface, the mission processor 206 obtains the current
position and obtains a waypoint from the ship to enable it to return to
the ship.

[0138] The move to waypoint process 254 is used to execute a mission.
Until the mission is complete and a mission finished process 264 is
executed, the move to waypoint process 254 sends a waypoint list to the
trajectory control 216, gets the current position from the trajectory
control 216, determines if the payload 208 should be activated (e.g. to
obtain data pertaining to the surroundings), maintains the payload 208 at
a specified ping rate or turns off the payload. A waypoint reached
function 262 determines when the waypoint has been reached and returns to
the move to waypoint process 254 to determine the next waypoint in the
mission. A timeout check function 256 can be used to determine if too
much time has elapsed in order to reach a waypoint. The overall process
then returns to the move to waypoint process 254 to recalibrate the
trajectory to the waypoint that has not been achieved. If the timeout
check 256 indicates that the underwater vehicle 3 has not reached its
desired waypoint within a timeout period, then a surface process 258 is
executed, which is also executed once the mission finish process 264 is
executed. The timeout period is typically calculated or determined during
the mission planning stage and is the estimated travel time of the
underwater vehicle 3 between waypoints. For example, the timeout period
is calculated based on the speed of the underwater vehicle 3, the
distance between waypoints, and a percentage error. In another
embodiment, if the timeout check 256 determines that the underwater
vehicle 3 has not reached the desired waypoint within the desired timeout
period, then the underwater vehicle 3 may be programmed to skip the
desired waypoint and attempt to reach the next waypoint instead. If it
still cannot reach the next waypoint, then it may be concluded that the
mission has not been programmed correctly, and the underwater vehicle 3
is attempting to reach waypoints within an unreasonable amount of time,
or some other factor is preventing the vehicle 3 from reaching the
waypoint. Other factors include, for example, a particularly strong head
current that slows down the vehicle 3, or a subsea obstacle entangling
the vehicle 3. Examples of subsea obstacles include fishing line, nets,
kelp, etc. The surface process 258 can also be executed if a
battery/health check process 260 indicates that the underwater vehicle 3
is low on battery power or has some other fault. The surface process 258
then triggers the return to ship process 252 which is shown twice in FIG.
28 for clarity.

[0139] The following Table 4 illustrates various mission fault conditions.

[0140] The following pseudo-code illustrates an example implementation of
the processes shown in FIG. 28.

TABLE-US-00006
while(watch dog timer)
{
sendLocation( ) send AUV position to surface
receiveCommand( )
case
command = directControl
send command to Motors
Fore: Rudder, Elevator, Thruster
Aft: Rudder, Elevator, Thruster
Check for obstacles using altimeters
loss of communication protection
stop (set waiting period) and surface
command = waypoint_mission
while mission not complete
send waypoint list to Trajectory control
get current position from TrajectoryControl
check if payload should be activated at this
position
keep payload at specified ping rate
else turnoff payload
relative commands (heading speed)
command = pipefollowing
(low priority)
while mission not complete
get waypoint updates from payload and send
to trajectory control
(relative output, heading - speed)
get current position from TrajectoryControl
check if payload should be activated at this
position
keep payload at specified ping rate
else turnoff payload
command = return home
turn off payload
surface
get current position
set wait for waypoint from ship
command return ship
command emergency surface (for testing faults)
end
}

[0141] The above pseudo-code illustrates a "pipefollowing" command, which
as can be seen, operates in a manner similar to the "waypoint mission"
command but also communicates with the payload 208 to get waypoint
updates.

[0142] The following Table 5 illustrates various functions that can be
called in the software to execute the processes in FIG. 28.

[0143] The trajectory control process 242 obtains waypoints or paths from
the mission processor 206, and calculates trajectories for the control
process 244. The following pseudo-code illustrates an example
implementation of the trajectory control process 242.

[0144] As illustrated in the above pseudo-code, in the case where the
trajectory mode is go to waypoint, the trajectory control process 242
gets the waypoints and passes them to the control process 244. This can
include the location, depth or attitude mode, location tolerance, depth
tolerance or attitude tolerance, speed, timeout. The trajectory mode then
waits for a command to get the next waypoint. When the trajectory mode is
for heading and speed, the heading, speed, depth and time are returned.
When the trajectory mode is to move (e.g. while maintaining a specified
attitude--complex manoeuvres etc.), the heading, speed, pitch, roll, and
yaw are returned. When the trajectory mode indicates "station keep", the
position is sent to the control process 244, which includes the location,
depths and attitude, location tolerance, depth tolerance, pitch, roll,
and yaw.

[0145] The control process 242 obtains waypoints from the trajectory
control process 242, and attempts to minimize the error between the
target waypoint and current waypoint. The following functions may be
implemented: getWaypoint( ); calcPD_Heading( ); calcPD_Velocity( );
calcPI_Depth( ); calcPD_Pitch( ); and calcPI_distance( ). Various control
logic can be implemented to be used in the control process 242 as shown
in FIGS. 29 to 33.

[0146] Turning to FIG. 29, a controller for controlling the pitch of the
underwater vehicle 3 is shown. FIG. 30 illustrates a controller for
controlling the depth of the underwater vehicle 3. the depth controller
is an outer loop around the pitch controller. The pitch controller should
run at a faster update rate than the depth controller. The integral
module is used in this example to remove the steady state error. The
integrator value should have limits to prevent windup.

[0147] FIG. 31 illustrates a controller for controlling the heading of the
underwater vehicle 3 and FIG. 32 illustrates a controller for controlling
the velocity of the underwater vehicle 3. FIG. 33 shows a controller for
implementing position control based on distance to the next waypoint. The
velocity control is the inner loop that runs at a faster rate.

[0148] The motors process 248 sends commands to the motors calculated from
the output of the control process 244. The following pseudo-code can be
implemented for performing speed or torque control.

[0149] The sensor process 240 obtains the actual data from all the
sensors. The following functions can be implemented for the sensor
process 240: getGPS( ) getMRU( ), getDVL( ), getDepth( ), and
getAltimeter( ).

[0150] The vehicle monitor process 238 checks the health of the underwater
vehicle 3 and takes action if the system fails. The following pseudo-code
can be implemented for the vehicle monitor process 238 to perform various
example checks on the health and status of the underwater vehicle 3.

[0151] The following describes the various interfaces internally between
tasks and externally to sensors and communication links. All the external
communications to the sensors, motors, etc. over RS232, CAN bus or
Ethernet are specified below to illustrate the communication interfaces
and protocols for implementing the example shown in FIG. 25. The internal
communications between tasks are also described.

[0152] A suitable altimeter 156 has the following communication
specifications: RS232, 115200 bps, No Parity, 8 Data bits, 1 stop bit.
The altimeter 156 should respond to a "Switch Data" command at which the
head transmits, receives and sends its return data back to the command
program. To prevent interference with the payload (in particular when
sonar), the DVL 154 should be run in a "command step" mode where once a
start command is received by the DVL 154, the system will ping and output
the result only once. For the transmit power, an auto mode should be used
where the DVL 154 automatically adjusts its transmission power in the
process of a deployment. The DVL 154 is typically deployed with the
transducer facing down. The speed of sound which may be required for
certain calculations is known to vary according to the current
environment in the water. Therefore, the speed of sound can be determined
either from user input (e.g. from reading tables or using another
available source) or by calculating the speed of sound using depth,
temperature and salinity measurements.

[0154] Inertial instrumentation may also be used. The selected
communications mode should be the one that can output raw data from the
gyros, accelerometers and magnetometer at the fastest update rate
possible. Below is the example for an inertial sensor. A standard
communications structure is as follows in Tables 7 and 8 but it can be
appreciated that other structures may be implemented depending on the
equipment used:

[0157] An inertial navigation system (INS) can be used which calculates
position, velocity and attitude using high frequency data from the MRU,
which comprises of three accelerometers, three gyros and a three axis
compass. The INS is aided by the DVL 154, depth gauge and altimeter. The
INS is initialized on the surface using the GPS. Gyros can be integrated
and corrected by the compass and accelerometers (e.g. using an extended
Kalman filter). The DVL 154 is used to correct the velocity from the
integrated accelerometers, which helps calculate the gravity vector,
which can be subtracted from the accelerations so that body acceleration
can be calculated. Position is calculated using the DVL 154, attitude and
integrated accelerations.

[0158] A north, east, down navigation frame should be assumed where north
points toward the bow (front) of the underwater vehicle 3, east points
starboard (right), and down points down. Rotations are right hand rule
where the thumb points in the direction of the axis. Misalignment angles
between the INS and DVL 154 should be accurately calibrated. For INS/DVL
navigation, the 17 state vector that we want to estimate in this example
is defined as:

[0166] The system can be described by the following nonlinear differential
equations:

{dot over (x)}=f(x)+w

z=h(x)+v

[0167] The first equation is the state update equation where x is the
vector of states, f(x) is a nonlinear function of the states and w is a
random zero mean process. The noise process model is Q=E(ww.sup.T).

[0168] The second equation in the measurement update where v is a
zero-mean random process described by the measurement noise matrix R
which is defined as R=E(vv.sup.T).

[0169] The measurement equation in discrete form can be written as
z.sub.k=h(x.sub.k)+v.sub.k.

[0170] The system and measurement equations are nonlinear, therefore a
first order approximation is used for the system dynamic matrix F and the
measurement matrix H.

[0171] The fundamental matrix for the discrete Riccati equations, can be
approximated by the Taylor series expansion for exp(FTs):
.PHI..sub.k.apprxeq.I+FT.sub.s. The first step is to initialize the
initial states, this would be done while the underwater vehicle 3 is on
the surface. The attitude quaternions are initialized by taking the
measurements over a specified start up period while the underwater
vehicle 3 is as still as possible from the accelerometers to calculate a
gravity vector, the compass to get heading and the GPS to correct the
accelerometers for motion. The initial velocity should be near zero, if
not if would be initialized from the GPS. The position will also be
initialized from the GPS. The gyro bias and accelerometer bias would be
initialized by integrating the gyro and accelerometer respective outputs
over the start up period.

[0172] Once the estimator is initialized there are two main parts to the
estimator time update which will constantly update the states at a
specified rate and the measurement update which will be done when
measurements are available from different sensors. The gyros,
accelerometers and DVL 154 are integrated to give position and
orientation estimate. To get an accurate estimate of the attitude and
position of the underwater vehicle 3 the drift from the gyros and
accelerometers should be corrected for using external measurements from
the compass, DVL 154, USBL, altimeter and depth gauge.

[0173] For a time update, first the system state vector is updated:

{circumflex over (x)}.sub.k+1=.PHI..sub.kx.sub.k={circumflex over
(x)}.sub.k+FT.sub.s{circumflex over (x)}.sub.k.

[0179] For a measurement update, the measurement update equations are
calculated when a measurement is available. In the underwater vehicle 3
case, the measurement would be from the DVL, USBL, altimeter or depth
gauge pressure sensor. For each different sensor the measurement matrix H
will have to be calculated along with the following equations:

K.sub.k=P.sub.kH.sub.k.sup.T(H.sub.kP.sub.kH.sub.k.sup.T+R).sup.-1

{circumflex over (x)}.sub.k+1={circumflex over
(x)}.sub.k+K.sub.k(z.sub.k-H{circumflex over (x)}.sub.k)

[0188] The vehicle monitor monitors overall vehicle software and status to
make sure that vehicle is operating correctly, takes action if any
underwater vehicle 3 part is not working (i.e. navigation failure, would
execute emergency surface). The input from sensors would be: Pitch, Roll,
Yaw, Altitude, Velocity, Position when available from GPS. The output to
motors would be: Fore: Rudder, Elevator, Thruster; and Aft: Rudder,
Elevator, Thruster. The output to electrical distribution would be: turn
of malfunctioning systems. The input to the electrical distribution would
be: health of electrical systems (e.g. current draw, etc.). The failure
modes and actions would be: main computer failure--stop mission and
execute emergency surface, turn on emergency beacon; one thruster
failure--continue mission, but adjust control algorithm to compensate for
motor loss; and both thrusters fail--stop mission and execute emergency
surface, turn on emergency beacon.

[0189] As noted above, the payload 208 receives commands from mission
processor 206 to operate equipment such as sonar. The input from the
mission processor for sonar would be: range, ping rate, TVG, resolution.
If in pipeline following mode, the payload 208 should receive the
location of pipeline so that trajectory can be plotted.

[0190] Although the above has been described with reference to certain
specific embodiments, various modifications thereof will be apparent to
those skilled in the art as outlined in the appended claims.